VP9 screenshare: use CONSTRAINED_FROM_ABOVE_DROP mode
This mode was added by libvpx team specificaly for this usecase: if a
layer is dropped, all lower layers have to be dropped also.
This ensures that higher layers always have higher framerate than the
lower layers and stream is RTP compatible.
This CL also renames full_superframe_drop_ to !layer_buffering, as it
closer reflects the purpose of that flag (in screenshare mode, no
buffering is needed, because the highest layer is always present in the
superframe, yet, it's not a full-superframe dropping mode).
Bug: webrtc:10257
Change-Id: I2589bfd2b9b63de0e410f277a716276234993843
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/151764
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29155}
diff --git a/modules/video_coding/codecs/vp9/vp9_impl.cc b/modules/video_coding/codecs/vp9/vp9_impl.cc
index b57c98b..42ab4f7 100644
--- a/modules/video_coding/codecs/vp9/vp9_impl.cc
+++ b/modules/video_coding/codecs/vp9/vp9_impl.cc
@@ -233,6 +233,7 @@
.LibvpxVp9TrustedRateController()),
dynamic_rate_settings_(
RateControlSettings::ParseFromFieldTrials().Vp9DynamicRateSettings()),
+ layer_buffering_(false),
full_superframe_drop_(true),
first_frame_in_picture_(true),
ss_info_needed_(false),
@@ -703,27 +704,31 @@
}
memset(&svc_drop_frame_, 0, sizeof(svc_drop_frame_));
- dropping_only_base_layer_ = inter_layer_pred_ == InterLayerPredMode::kOn &&
- codec_.mode == VideoCodecMode::kScreensharing &&
- num_spatial_layers_ > 1;
- if (dropping_only_base_layer_) {
- // Screenshare dropping mode: only the base spatial layer
- // can be dropped and it doesn't affect other spatial layers.
- // This mode is preferable because base layer has low bitrate targets
- // and more likely to drop frames. It shouldn't reduce framerate on other
- // layers.
- svc_drop_frame_.framedrop_mode = LAYER_DROP;
+ const bool reverse_constrained_drop_mode =
+ inter_layer_pred_ == InterLayerPredMode::kOn &&
+ codec_.mode == VideoCodecMode::kScreensharing &&
+ num_spatial_layers_ > 1;
+ if (reverse_constrained_drop_mode) {
+ // Screenshare dropping mode: drop a layer only together with all lower
+ // layers. This ensures that drops on lower layers won't reduce frame-rate
+ // for higher layers and reference structure is RTP-compatible.
+ svc_drop_frame_.framedrop_mode = CONSTRAINED_FROM_ABOVE_DROP;
svc_drop_frame_.max_consec_drop = 5;
- svc_drop_frame_.framedrop_thresh[0] = config_->rc_dropframe_thresh;
- for (size_t i = 1; i < num_spatial_layers_; ++i) {
- svc_drop_frame_.framedrop_thresh[i] = 0;
+ for (size_t i = 0; i < num_spatial_layers_; ++i) {
+ svc_drop_frame_.framedrop_thresh[i] = config_->rc_dropframe_thresh;
}
+ // No buffering is needed because the highest layer is always present in
+ // all frames in CONSTRAINED_FROM_ABOVE drop mode.
+ layer_buffering_ = false;
} else {
// Configure encoder to drop entire superframe whenever it needs to drop
// a layer. This mode is preferred over per-layer dropping which causes
// quality flickering and is not compatible with RTP non-flexible mode.
svc_drop_frame_.framedrop_mode =
full_superframe_drop_ ? FULL_SUPERFRAME_DROP : CONSTRAINED_LAYER_DROP;
+ // Buffering is needed only for constrained layer drop, as it's not clear
+ // which frame is the last.
+ layer_buffering_ = !full_superframe_drop_;
svc_drop_frame_.max_consec_drop = std::numeric_limits<int>::max();
for (size_t i = 0; i < num_spatial_layers_; ++i) {
svc_drop_frame_.framedrop_thresh[i] = config_->rc_dropframe_thresh;
@@ -1017,7 +1022,7 @@
}
timestamp_ += duration;
- if (!full_superframe_drop_) {
+ if (layer_buffering_) {
const bool end_of_picture = true;
DeliverBufferedFrame(end_of_picture);
}
@@ -1399,7 +1404,7 @@
vpx_svc_layer_id_t layer_id = {0};
vpx_codec_control(encoder_, VP9E_GET_SVC_LAYER_ID, &layer_id);
- if (!full_superframe_drop_) {
+ if (layer_buffering_) {
// Deliver buffered low spatial layer frame.
const bool end_of_picture = false;
DeliverBufferedFrame(end_of_picture);
@@ -1441,7 +1446,7 @@
vpx_codec_control(encoder_, VP8E_GET_LAST_QUANTIZER, &qp);
encoded_image_.qp_ = qp;
- if (full_superframe_drop_) {
+ if (!layer_buffering_) {
const bool end_of_picture = encoded_image_.SpatialIndex().value_or(0) + 1 ==
num_active_spatial_layers_;
DeliverBufferedFrame(end_of_picture);
@@ -1455,10 +1460,8 @@
if (num_spatial_layers_ > 1) {
// Restore frame dropping settings, as dropping may be temporary forbidden
// due to dynamically enabled layers.
- svc_drop_frame_.framedrop_thresh[0] = config_->rc_dropframe_thresh;
- for (size_t i = 1; i < num_spatial_layers_; ++i) {
- svc_drop_frame_.framedrop_thresh[i] =
- dropping_only_base_layer_ ? 0 : config_->rc_dropframe_thresh;
+ for (size_t i = 0; i < num_spatial_layers_; ++i) {
+ svc_drop_frame_.framedrop_thresh[i] = config_->rc_dropframe_thresh;
}
}
diff --git a/modules/video_coding/codecs/vp9/vp9_impl.h b/modules/video_coding/codecs/vp9/vp9_impl.h
index f0dac27..19c77b6 100644
--- a/modules/video_coding/codecs/vp9/vp9_impl.h
+++ b/modules/video_coding/codecs/vp9/vp9_impl.h
@@ -125,8 +125,8 @@
bool external_ref_control_;
const bool trusted_rate_controller_;
const bool dynamic_rate_settings_;
+ bool layer_buffering_;
const bool full_superframe_drop_;
- bool dropping_only_base_layer_;
vpx_svc_frame_drop_t svc_drop_frame_;
bool first_frame_in_picture_;
VideoBitrateAllocation current_bitrate_allocation_;
